FIELD OF THE INVENTION
The present invention is related to methods for recovering a hydrogen-rich gas stream from a hydrogen and hydrocarbon effluent of a catalytic hydrocarbon conversion zone. In addition this invention improves the recovery of liquifiable hydrocarbons from hydrogen and hydrocarbon effluent streams.
Various types of catalytic hydrocarbon conversion reaction systems have found widespread utilization throughout the petroleum and petrochemical industries for effecting the conversion of hydrocarbons to different products. The reactions employed in such systems are either exothermic or endothermic, and of more importance to the present invention, often result in either the net production of hydrogen or the net consumption of hydrogen. Such reaction systems, as applied to petroleum refining, have been employed to effect numerous hydrocarbon conversion reactions including those which predominate in catalytic reforming, ethylbenzene dehydrogenation to styrene, propane and butane dehydrogenation, etc.
Petroleum refineries and petrochemical complexes customarily comprise numerous reaction systems. Some systems within the refinery or petrochemical complex may result in the net production of hydrogen. Because hydrogen is relatively expensive, it has become the practice within the art of hydrocarbon conversion to supply hydrogen from reaction systems which result in the net production of hydrogen to reaction systems which are net consumers of hydrogen. Occasionally, the net hydrogen being passed to the net hydrogen-consuming reactions systems must be of high purity due to the reaction conditions and/or the catalyst employed in the systems. Such a situation may require treatment of the hydrogen from the net hydrogen-producing reaction systems to remove hydrogen sulfide, light hydrocarbons, etc. from the net hydrogen stream.
Alternatively, the hydrogen balance for the petroleum refinery or petrochemical complex may result in excess hydrogen, i.e., the net hydrogen-producing reaction systems produce more hydrogen than is necessary for the net hydrogen-consuming reaction systems. In such an event, the excess hydrogen may be sent to the petroleum refinery or petrochemical complex fuel system. However, because the excess hydrogen often has admixed therewith valuable components, such as C.sub.3 + hydrocarbons, it is frequently desirable to treat the excess hydrogen to recover these components prior to its passage to fuel.
Typical of the net hydrogen-producing hydrocarbon reaction systems are catalytic reforming, catalytic dehydrogenation of alkylaromatics and catalytic dehydrogenation of paraffins. Commonly employed net hydrogen-consuming reaction systems are hydrotreating, hydrocracking and catalytic hydrogenation. Of the above-mentioned net hydrogen-producing and consuming hydrocarbon reaction systems, catalytic reforming ranks as one of the most widely employed. By virtue of its wide application and its utilization as a primary source of hydrogen for the net hydrogen-consuming reactions systems, catalytic reforming has become well known in the art of hydrocarbon conversion reaction systems.
It is well known that high quality petroleum products in the gasoline boiling range including, for example, aromatic hydrocarbons such as benzene, toluene and the xylenes, are produced by the catalytic reforming process wherein a naphtha fraction is passed to a reaction zone wherein it is contacted with a platinum-containing catalyst in the presence of hydrogen. Generally, the catalytic reforming reaction zone effluent, comprising gasoline boiling range hydrocarbons and hydrogen, is passed to a vapor-liquid equilibrium separation zone and is therein separated into a hydrogen-containing vapor phase and an unstabilized hydrocarbon liquid phase. A portion of the hydrogen-containing vapor phase may be recycled to the reaction zone. The remaining hydrogen-containing vapor phase is available for use either by the net hydrogen-consuming processes or as fuel for the petroleum refinery or petrochemical complex fuel system. While a considerable portion of the hydrogen-containing vapor phase is required for recycle purposes, a substantial net excess is available for the other uses.
Because the dehydrogenation of naphthenic hydrocarbons is one of the predominant reactions of the reforming process, substantial amounts of hydrogen are generated within the catalytic reforming reaction zone. Accordingly, a net excess of hydrogen is available for use as fuel or for use in a net hydrogen-consuming process such as the hydrotreating of sulfur-containing petroleum feedstocks. However, catalytic reforming also involves a hydrocracking function among the products of which are relatively low molecular weight hydrocarbons including methane, ethane, propane, butanes and the pentanes, substantial amounts of which appear in the hydrogen-containing vapor phase separated from the reforming reaction zone effluent. These normally gaseous hydrocarbons have the effect of lowering the hydrogen purity of the hydrogen-containing vapor phase to the extent that purification is often required before the hydrogen is suitable for other uses. Moreover, if the net excess hydrogen is intended for use as fuel in the refinery or petrochemical complex fuel system, it is frequently desirable to maximize the recovery of C.sub.3 + hydrocarbons which are valuable as feedstock for other processes.
Many processes for the purification of hydrogen-rich gas streams from the effluent of hydrocarbon conversion reaction zones are disclosed. U.S. Pat. No. 3,431,195, issued Mar. 4, 1969, discloses a process wherein the hydrogen and hydrocarbon effluent of a catalytic reforming zone is first passed to a low pressure vapor-liquid equilibrium separation zone from which zone is derived a first hydrogen-containing vapor phase and a first unstabilized hydrocarbon liquid phase. The hydrogen-containing vapor phase is compressed and recontacted with at least a portion of the liquid phase and the resulting mixture is passed to a second high pressure vapor-liquid equilibrium separation zone. Because the second zone is maintained at a higher pressure, a new vapor liquid equilibrium is established resulting in a hydrogen-rich gas phase and a second unstabilized hydrocarbon liquid phase. A portion of the hydrogen-rich vapor phase is recycled back to the catalytic reforming reaction zone with the balance of the hydrogen-rich vapor phase being recovered as a hydrogen-rich gas stream relatively free of C.sub.3 -C.sub.6 hydrocarbons.
U.S. Pat. No. 3,516,924, issued Jun. 23, 1970, discloses a system wherein the reaction zone effluent from a catalytic reforming process is first separated in a vapor-liquid equilibrium separation zone to produce a hydrogen-containing vapor phase and an unstabilized liquid hydrocarbon phase. The two phases are again recontacted and again separated in a higher pressure vapor-liquid equilibrium separation zone. A first portion of the resulting hydrogen-rich vapor phase is recycled back to the catalytic reforming zone while the remaining portion of the hydrogen-rich vapor phase is passed to an absorber column in which stabilized reformate is utilized as the sponge oil. A high purity hydrogen gas stream is recovered from the absorption zone and the sponge oil, containing light hydrocarbons, is recontacted with the hydrocarbon liquid phase from the first vapor-liquid equilibrium separation zone prior to the passage thereof to the second high pressure vapor-liquid equilibrium separation zone.
U.S. Pat. No. 3,520,800, issued Jul. 14, 1970, discloses a method of obtaining a hydrogen-rich gas stream from a catalytic reforming reaction zone effluent. As in the previously discussed methods, the reforming reaction zone effluent is passed to a first vapor-liquid equilibrium separation zone from which is obtained a first hydrogen-containing vapor phase and a first unstabilized hydrocarbon liquid phase. The hydrogen-containing vapor phase is compressed and recontacted with the hydrocarbon liquid phase. Thereafter the mixture is passed to a second vapor-liquid equilibrium separation zone maintained at a higher pressure than the first vapor-liquid equilibrium separation zone. A second hydrogen-containing vapor phase of higher hydrogen purity is recovered from the second vapor-liquid equilibrium separation zone with a portion thereof being recycled back to the catalytic reforming reaction zone. The remaining amount of the resulting hydrogen-containing vapor phase is passed to a cooler wherein the temperature of the phase is reduced at least 20.degree. F. lower than the temperature maintained in the second vapor-liquid equilibrium separation zone. After cooling, the hydrogen phase is passed to a third vapor-liquid equilibrium separation zone from which a high purity hydrogen gas stream is recovered.
U.S. Pat. No. 3,520,799, issued Jul. 14, 1970, discloses yet another method for obtaining a high purity hydrogen gas stream from a catalytic reforming reaction zone effluent. As in all the previous schemes, the reaction zone effluent is passed to a low pressure vapor-liquid equilibrium separation zone from which is produced a hydrogen-containing vapor phase and an unstabilized liquid hydrocarbon phase. After compression, the hydrogen-containing vapor phase is recontacted with the unstabilized liquid hydrocarbon phase and the resulting mixture is passed to a high pressure vapor-liquid equilibrium separation zone. A second hydrogen-containing vapor phase is produced of higher purity than the hydrogen-containing vapor phase from the low pressure vapor-liquid equilibrium separation zone. A first portion of this higher purity hydrogen-containing vapor phase is recycled back to the catalytic reforming zone. The balance of the higher purity hydrogen-containing vapor phase is passed to an absorption zone where it is contacted with a lean sponge oil preferably comprising C.sub.6 + hydrocarbons. A hydrogen-containing gas stream is removed from the absorber and after cooling, passed to a third vapor-liquid equilibrium separation zone. The sponge oil, containing constituents absorbed from the higher purity hydrogen-containing vapor phase is removed from the absorption zone and is admixed with the unstabilized liquid hydrocarbon stream from the low pressure vapor-liquid equilibrium separation zone prior to the recontacting thereof with the compressed hydrogen-containing vapor phase. A stream of high purity hydrogen gas is removed from the third vapor-liquid equilibrium separation zone.
U.S. Pat. No. 3,882,014, issued May 6, 1975, discloses another method of obtaining a high purity hydrogen stream from the reaction zone effluent of a catalytic reforming process. The catalytic reforming reaction zone effluent is first passed to a vapor-liquid equilibrium separation zone from which is recovered an unstabilized liquid hydrocarbon stream and a hydrogen-containing vapor phase. After compression, the hydrogen-containing vapor phase is passed to an absorption zone wherein it is contacted with a sponge oil comprising stabilized reformate. A high purity hydrogen gas stream is recovered from the absorption zone with one portion thereof being recycled back to the catalytic reforming reaction zone while the remainder is recovered for further use. A liquid stream is recovered from the absorption zone and admixed with the unstabilized liquid hydrocarbon stream from the vapor-liquid equilibrium separation zone. The admixture is then fractionated in a stabilizing column to produce the stabilized reformate, a first portion of which is utilized as the sponge oil in the absorption zone.
U.S. Pat. No. 4,212,726, issued Jul. 15, 1980, discloses a method for recovering high purity hydrogen streams from catalytic reforming reaction zone effluents wherein the reaction zone effluent from the catalytic reforming process is passed to a first vapor-liquid equilibrium separation zone from which is recovered a first unstabilized hydrocarbon stream and a first hydrogen-containing vapor stream. After compression, the hydrogen-containing vapor stream is passed to an absorption column wherein it is contacted with the first liquid hydrocarbon phase from the vapor-liquid equilibrium separation zone and stabilized reformate. A high purity hydrogen gas stream is recovered from the absorption zone with one portion being recycled back to the reaction zone and the balance being recovered for further use.
U.S. Pat. No. 4,364,820, issued Dec. 21, 1982, discloses a method of recovering high purity hydrogen gas from a catalytic reforming reaction zone effluent wherein the reaction zone effluent is first separated in a vapor-liquid equilibrium separation zone into a first hydrogen-containing vapor phase and a first liquid hydrocarbon phase. One portion of the first hydrogen-containing vapor phase is compressed and recycled back to the catalytic reaction zone. The balance of the hydrogen-containing vapor phase is compressed and contacted with a second liquid hydrocarbon phase recovered from a hereinafter described third vapor-liquid equilibrium separation zone. The admixture is then passed to a second vapor-liquid equilibrium separation zone from which is derived a third liquid hydrocarbon phase comprising unstabilized reformate and a second hydrogen-containing vapor phase of higher purity than the first hydrogen-containing vapor phase derived from the first vapor-liquid equilibrium separation zone. The second hydrogen-containing vapor phase is subjected to compression and then contacted with the first liquid hydrocarbon phase from the first vapor-liquid equilibrium separation zone. The resulting admixture is then passed to a third vapor-liquid equilibrium separation zone from which is derived a hydrogen gas stream of high purity and the aforementioned second liquid hydrocarbon phase.
U.S. Pat. No. 4,374,726, issued Feb. 22, 1983, discloses a further method of obtaining a high purity hydrogen gas stream from the reaction zone effluent of a catalytic reforming process. In this reference, the reaction zone effluent is passed to a vapor-liquid equilibrium separation zone to produce a first hydrocarbon liquid phase and a hydrogen-containing vapor phase. A first portion of the hydrogen-containing vapor phase is compressed and recycled to the catalytic reforming reaction zone. A second portion of the hydrogen-containing vapor phase is compressed and thereafter recontacted with the first liquid hydrocarbon phase from the vapor-liquid equilibrium separation zone. The resulting admixture is then passed to a second vapor-liquid equilibrium separation zone to produce a hydrogen gas stream of high purity and a second liquid hydrocarbon phase comprising unstabilized reformate.
U.S. Pat. No. 4,568,451, issued Feb. 4, 1986 discloses a method of recovering high purity hydrogen gas from a catalytic reforming reaction zone effluent wherein the reaction zone effluent is first separated in a vapor-liquid equilibrium separation zone into a first hydrogen-containing vapor phase and a first unstabilized liquid hydrocarbon phase. One portion of the first hydrogen-containing vapor phase is compressed and recycled back to the catalytic reaction zone. The balance of the hydrogen-rich vapor phase is admixed with a portion of the first unstabilized liquid reformate chilled and passed to an equilibrium separator from which a hydrogen-rich vapor phase and a second liquid hydrocarbon phase comprising unstabilized reformate are recovered.
In addition to the above-mentioned patent literature, the technical literature within the art has also disclosed methods for separating reaction zone effluents to obtain hydrogen-containing gas streams. For example, the Nov. 10, 1980 issue of the Oil and Gas Journal discloses an LPG dehydrogenation process in which the entire reaction zone effluent is first dried, then subjected to indirect heat exchange with a cool hydrogen-containing gas stream. The cool hydrogen-containing gas stream is derived by passing the entire cooled reaction zone effluent to a vapor-liquid equilibrium separation zone. The hydrogen-containing gas stream is removed from the separation zone and is then expanded. Thereafter it is subjected to indirect heat exchange with the entire reaction zone effluent. After the indirect heat exchange step, a portion of the hydrogen-containing vapor phase is recycled to the reaction zone.
The many art references have shown many similar arrangements of chillers, separators, absorbers, compressors, and heat exchange equipment for recovering a hydrogen-rich gas stream and liquifiable hydrocarbon components from a hydrocarbonaceous effluent of a catalytic conversion zone. Out of the many combinations of such components that can be used, it has been discovered that a particular arrangement of separators and refrigeration equipment will dramatically improve the recovery of liquifiable hydrocarbons in such a system with only a relatively simple arrangement of components.